The heart of a computer is a magnetic disk drive which includes a rotating magnetic disk, a slider that has an assembly of write and read heads, a suspension arm above the rotating magnetic disk, and an actuator arm that swings the suspension arm to place the assembly of write and read heads over selected circular tracks on the rotating magnetic disk. When the magnetic disk is stationary, the suspension arm biases the slider into contact with the surface of the magnetic disk. When the magnetic disk rotates, air is swirled by the rotating magnetic disk, causing the slider to ride on an air bearing a slight distance from the surface of the rotating magnetic disk. When the slider rides on the air bearing, the assembly of write and read heads is employed for writing magnetic impressions to and reading magnetic signal fields from the rotating magnetic disk. The assembly of write and read heads is connected to processing circuitry that operates according to a computer program to implement the write and read functions.
A commonly used write head includes first and second write-pole layers, a write-gap layer, a coil layer, and first, second and third insulation layers. The write-gap, coil and insulation layers are sandwiched between the first and second write-pole layers. The first and second write-pole layers are connected at the back of the write head. Current conducted to the coil layer induces a magnetic flux in the first and second write-pole layers which cause a magnetic field to fringe out at the air bearing surface of the write head for the purpose of writing the aforementioned magnetic impressions in circular tracks on the aforementioned rotating magnetic disk.
A commonly used read head 100, as shown in FIG. 1, includes Ni—Fe first and second shield layers 102, 104, Al2O3 first and second read-gap layers 106, 108, a giant magnetoresistance (GMR) sensor 110 in a read region, and side longitudinal bias (LB) stacks 130 in two side regions. The GMR sensor 110 and the side longitudinal bias stacks 130 are sandwiched between the first ad second read-gap layers 106, 108, which are in turn sandwiched between the first and second shield layers 102, 104. The GMR sensor 110 typically comprises Al—O/Ni—Cr—Fe/Ni—Fe seed layers 112, an antiferromagnetic Pt—Mn transverse pinning layer 114, a transverse flux-closure structure 116 (comprising a ferromagnetic Co—Fe keeper layer 118, a nonmagnetic Ru spacer layer 120, and a ferromagnetic Co—Fe reference layer 122), a nonmagnetic conducting Cu—O spacer layer 124, ferromagnetic Co—Fe/Ni—Fe sense layers 126, and a nonmagnetic Ta cap layer 128.
The side LB stack 130 typically comprises a nonmagnetic Cr seed layer 132, a hard-magnetic Co—Pt—Cr longitudinal bias layer 134, and a nonmagnetic Rh conductor layer 136.
In the prior-art fabrication process of the read head 100, the GMR sensor 110 comprising Al—O(3)/Ni—Cr—Fe(3.2)/Ni—Fe(0.4)/Pt—Mn(15)/Co—Fe(1.6)/Ru(0.8)/Co—Fe (1.6)/Cu—O(1.8)/Co—Fe(1)/Ni—Fe(1.6)/Ta(4) films (thickness in nm) is deposited in a deposition field of 100 Oe on a 8.2 nm thick Al2O3 first read-gap layer 102. A transverse-field anneal is applied in a field of 50,000 Oe for 5 hours at 265° C. in a transverse direction perpendicular to the deposition field. A monolayer photoresist is then applied and patterned in a photolithographic tool to mask the GMR sensor 110 in a read region. Ion milling is applied to entirely remove the GMR sensor 110 and partially remove the Al2O3 first read-gap layer 106 in the exposed side regions, in order to form sharp contiguous junctions at the read and side regions. The longitudinal bias stack 130, comprising the Cr(15) seed layer 132, the Co—Pt—Cr(10) longitudinal bias layer 134 and the Rh(45) conductor layer 136, is then deposited preferably with ion beam sputtering at a normal angle for abutting the GMR sensor 110 at the sharp contiguous junctions. The monolayer photoresist is lifted off, with assistance of chemical mechanical polishing (CMP), and the Al2O3(8.2) second read-gap layer 104 is then deposited.
The GMR sensor 110 requires the transverse-field anneal to develop strong antiferromagnetic/ferromagnetic coupling between the Pt—Mn transverse pinning layer 114 and the transverse flux-closure structure 116. The anneal field must exceed the saturation field (HS) of antiparallel ferromagnetic/ferromagnetic coupling across the Ru spacer layer 120 (˜8,000 Oe) for aligning the magnetizations of the Co—Fe keeper and reference layers 118, 122 in the transverse direction. After cooling to room temperature, the magnetization of the Co—Fe keeper layer 118 is rigidly pinned by the Pt—Mn transverse pinning layer 114 in the transverse direction, while the magnetization of the Co—Fe reference layer 122 is rotated by 180°. A transverse flux closure will be formed between the magnetization of the Co—Fe keeper and reference layers 118, 112 after patterning and lapping, resulting in a small net magnetic moment in the transverse flux-closure structure 116. This small magnetic moment induces a small demagnetizing field (HD) in the Co—Fe/Ni—Fe sense layers 126.
In the GMR sensor 110, antiferromagnetic/ferromagnetic coupling occurs between the Pt—Mn transverse pinning layer 114 and the Co—Fe/Ru/Co—Fe transverse flux-closure structure 116, producing a pinning field (HP). This HP must be high enough to rigidly pin the net magnetization of the Co—Fe/Ru/Co—Fe transverse flux-closure structure 116 in a transverse direction perpendicular to the ABS for proper sensor operation. Ferromagnetic/ferromagnetic coupling also occurs across the Cu—O spacer layer 124, producing a negative ferromagnetic coupling field (HF). This HF must be precisely controlled so that the sum of HF and HD counterbalances a current-induced field (H1) in the Co—Fe/Ni—Fe sense layer 126 (HF+HD=H1), thereby orienting the magnetization of the Co—Fe/Ni—Fe sense layers 126 in a longitudinal direction parallel to the ABS for optimally biased sensor operation.
During sensor operation, only the magnetization of the Co—Fe/Ni—Fe sense layers 126 is free to rotate in positive and negative directions from a quiescent state in response to positive and negative magnetic signal fields from the adjacent rotating magnetic disk. This rotation causes changes in scattering of conduction electrons at interfaces of the Cu—O spacer layer 124 with the sense and reference layers 126, 122, thereby causing changes in the resistance of the GMR sensor 110 in proportion to cos θ, where θ is an angle between the magnetizations of the sense and reference layers 126, 122. The changes in the resistance of the GMR sensor 110 cause potential changes that are detected and processed as playback signals.
There are several disadvantages in the use of the GMR sensor 110 with the hard magnetic stabilization scheme as described in the prior art. First, to attain stable GMR responses, the Cr seed layer 132 in the side regions must be thick enough to align the midplane of the Co—Pt—Cr longitudinal bias layer 134 with that of the Co—Fe/Ni—Fe sense layers 126 of the GMR sensor 110. However, the Cr seed layer 132 at the contiguous junctions is thus inevitably thick, causing substantial separation between the sense layers 126 and the Co—Pt—Cr longitudinal bias layer 134, and significantly reducing stabilization efficiency. Second, the Rh conductor layer 136 must be thick enough to provide a low-resistance path. As a result, substantial overhangs at sides of the monolayer photoresist are formed, causing difficulties in the liftoff process. Third, the CMP that is typically applied to facilitate the liftoff process may cause mechanical and magnetic damages to the GMR sensor 110. Fourth, in this hard magnetic stabilization scheme, longitudinal bias fields provided by the Co—Pt—Cr longitudinal bias layer 134 are high at edges of the Co—Fe/Ni—Fe sense layers 126, causing difficulties in rotating the magnetization of the Co—Fe/Ni—Fe sense layers 126, but are low at the center of the Co—Fe/Ni—Fe sense layers 126, causing difficulties in stabilizing the Co—Fe/Ni—Fe sense layers 126. To eliminate these disadvantages, a novel antiferromagnetic stabilization scheme is proposed in this invention.